This invention relates to the field of corrosion reduction and fluid leakage in process piping. This invention also relates to the field of process control.
The prior art has recognized the need for special methods for handling many different types of fluid processing units. These units are useful for converting a less desirable inlet fluid stream into a more desirable outlet fluid stream. For example some fluid processing units take streams containing highly toxic materials and convert them into streams containing safe materials, some units convert waste streams into valuable streams which can be sold, and some units convert low value streams of fluids into higher value streams of fluids. These types of units are often placed in service where either because of cost or space limitations it is highly desirable that the unit operate 100% of the time. Unfortunately, in practical applications, these types of units must sometimes be shut down for example to regenerate a catalyst, regenerate an absorbent, replace broken equipment, install new equipment or to provide for the safety of human operators and the environment around the unit. In many instances, during the period the unit is incapable of processing fluid, some means must be employed whereby the process fluid can be routed to other units for processing or to storage for later processing by the original unit. These means for routing process fluid around units during the times that the unit it unavailable are herein referred to as a bypass means since these means provide a way for fluids to bypass their normal routes of processing and flow instead through alternative routes.
Often the process fluids are corrosive or contain corrosive substances so that equipment used in the fluid processing units and in the bypass means must be impervious to, or at least resistant to corrosion from the process fluid. The prior art has recognized that excessive corrosion may occur when corrosive fluids are left in contact with materials used to construct these processing units and fluid bypass means. The prior art has also recognized that most bypass means are actually in use a small percentage of the time and that it is highly advantageous to drain the corrosive fluid from the bypass means during extended periods of nonuse in order to prevent some corrosion that would otherwise occur. One common type of bypass means used to achieve this result is termed a double block and bleed system wherein the bypass means is a conduit which can be blocked-in preventing flow through the conduit, with provisions to thereafter drain (bleed) the fluid in the blocked-in portion.
One of the disadvantages of this type of arrangement is that when valves are located on the ends of the conduit and are closed to form the blocked-in portion, these valves may leak and process fluid may again enter the conduit subjecting the conduit to additional corrosion. Another disadvantage to the double block and bleed apparatus is that sometimes additional storage facilities or expensive additional processing units are required to store or process the fluid which is bled from the blocked-in conduit. Another disadvantage of the double block and bleed type apparatus is that fluid which may leak through the closed valves may not only corrode the process piping but may also cause additional problems for other downstream units or for the atmosphere to which it is passed.